As is well known in the art, disposable paperboard containers (e.g., beverage cups) have a generally tubular side wall joined to a planar bottom wall along a circumferential seam. Typically, the tubular side wall will be slightly tapered so that its diameter at the upper open end is greater as compared to the diameter at the bottom wall. In addition, the containers will typically have an integral outwardly curled portion circumferentially extending along the side wall's upper edge to thereby form an upper lip of the container. This so-called "top-curl" is especially desirable if the container is in the form of a beverage cup as it increases the rigidity of the cup along the circumferential upper edge of the side wall as well as promoting increased comfort when the beverage is consumed.
It is oftentimes desirable to further increase the circumferential rigidity of paperboard containers by application of a localized "loading" of the top curl with a relatively volumetrically heavy amount of coating material. In this manner, the circumferential rigidity of the container may be increased at minimal costs since the use of relatively more heavy grades of paperboard stock and/or the application of greater amounts of coating material onto the surfaces of the container may be avoided. Thus, localized application of coating material onto the top curl of paperboard containers represents an attractive means for increasing container rigidity at minimal additional manufacturing costs.
Techniques to apply a localized amount of a coating material to the top curls of paperboard containers have been disclosed in commonly owned U.S. patent application Ser. No. 07/550,821 filed Jul. 11, 1990 (now U.S. Pat. No. 5,078,313), the entire content of which is expressly incorporated hereinto by reference. According to one of the disclosed techniques, a wax nozzle is arranged so as to direct a stream of atomized molten wax material along a circumferential region that corresponds to the container top curl. Another disclosed technique is to establish a continual flowing layer of molten wax through which the top curl of an inverted cup may be rotated.
The present invention is generally directed to another technique whereby a relatively heavy application of liquid-impermeable material may be applied locally to the top curls of paperboard containers. In this regard, the present invention is broadly embodied in a top curl applicator assembly having a porous applicator which may be saturated with molten coating material. The applicator assembly is especially adapted to contact the top curl of paperboard containers so that an amount of the molten coating material which saturates the porous applicator may be transferred to the top curl and thereby increase the top curl's circumferential rigidity upon solidification.
In preferred embodiments, the applicator assembly will be positioned laterally parallel of a linear treatment path along which the containers are conveyed in an inverted manner. Each container is rotated during conveyance along the linear treatment path such that the entire circumference of the top curl is brought into contact with the elongate porous applicator saturated with molten coating material. Preferably, the container is rotated in contact with the applicator a successive number of turns so that a corresponding successive amount of coating layers may be applied to the top curl. The coating material will be transferred to the top curl due to the wiping contact that occurs between the rotating top curl and the stationary applicator. The amount of the coating material that is transferred to the container top curl may be controllably selected by varying the dwell time that the top curl remains in contact with the saturated applicator, which can be achieved, for example, by varying the rotation speed of the container, the linear speed at which the container travels along the treatment path, the length of the applicator and/or the amount of coating material that is present in the saturated applicator.
Further aspects and advantages of this invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiment thereof.